Method for installing an electric conductor in a drill string

ABSTRACT

A method for installing an electric conductor in a drill string during drilling operations wherein an insulated electric conductor is lowered into the drill string and thereafter the drill string and conductor are lengthened as the borehole is advanced by adding lengths of pipe and conductor sections to the drill string and conductor, respectively.

United States Patent [191 Heilhecker et al.

[ METHOD FOR INSTALLING AN ELECTRIC CONDUCTOR IN A DRILL STRING [75]Inventors: Joe Keith l-leilhecker; Donald Bayne Wood, both of Houston,Tex.

[73] Assignee: Esso Production Research Company,

Houston, Tex.

221 Filed: Apr. 12, 1973 211 App]. No.: 350,674

52 us. Cl 166/315, 166/65, 175/50, 339/16 51 Int. Cl. E2lb 47/12 58Field 61 Search 166/315, 65; 17s/40-50, 104; 174/47 [56] ReferencesCited UNlTED STATES PATENTS 2,096,279 10/1937 Karcher 174/47 [451Apr.'30, 1974 2,339,274 1/1944 Kothny 1. 339/16 2,370,818 3/1945Silverrnan 175/40 2,650,067 8/1953 Martin 175/50 2,748,358 5/1956Johnston 339/16 3,285,629 11/1966 Cullen et al. 175/104 PrimaryExaminer-James A. Leppink Attorney, Agent, or Firm-Robert L. GrahamABSTRACT A method for installing an electric conductor in a drill stringduring drilling operations wherein an insulated electric conductor islowered into the drill string and thereafter the drill string andconductor are lengthened as the borehole is advanced by adding lengthsof pipe and conductor sections to the drill string and conductor,respectively.

12 Claims, 12 Drawing Figures PATNTEBAPR30 1914 SHEET 3 BF 4 wzOEbmmFIG.8

FIG. IO

METHOD FOR INSTALLING AN ELECTRIC CONDUCTOR IN A DRILL STRING BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates to animproved method for performing wellbore telemetry operations. In oneaspect it relates to a method for installing an insulated electricconductor in a pipe string used in rotary drilling operations.

2. Description of the Prior Art In the drilling of oil wells, gas wells,and similar boreholes, it frequently is desirable to transmit electricenergy between subsurface and surface locations. One application whereelectrical transmission has received considerable attention in recentyears is in wellbore telemetry systems designed to sense, transmit, andreceive information indicative of a subsurface condition. This operationhas become known in the art as logging while drilling.

A major problem associated with wellbore telemetry systems has been thatof providing reliable means for transmitting an electric signal betweenthe subsurface and surface location. This problem can best beappreciated by considering the manner in which rotary drillingoperations are normally performed. In conventional rotary drilling, aborehole is advanced by rotating a drill string provided with a drillbit. Lengths of drill pipe, usually about 30 feet long, are added to thedrill string one at a time as the borehole is advanced in increments. Inadapting an electric telemetry system to rotary drilling equipment, themeans for transmitting the electric signal through the drill string mustbe such to permit the connection of additional pipe lengths to the drillstring as the borehole is advanced. An early approach to the probleminvolved the use of continuous electric cable which was adapted to belowered inside the drill string and to make contact with a subsurfaceterminal. This technique, however, required withdrawing the cable fromthe drill string each time a pipe section was added to the drill string.A more recent approach involves the use of special drill pipe equippedwith an electric conductor. Ea'ch pipe section is provided withconnectors which mate with connectors of an adjacent pipe section andthereby provide an electric circuit across the joint (see US. Pat. Nos.3,518,608 and 3,518,609). Disadvantages of this system include the highcost of the special pipe sections, the need for a large number ofelectric connections (one at each joint), and the difficulty ofmaintaining insulation of the electric connectors at each joint.

SUMMARY OF THE INVENTION The purpose of the present invention is toprovide an electric circuit between a subsurface location in a well andthe surface. The invention permits the monitoring of a subsurfacecondition or the actuation of a subsurface instrument as drillingoperations are in progress.

Briefly, the method involves lowering a drill string in a well byconnecting a plurality of pipe sections together in end-to-end relation,lowering an insulated electric conductor in the drill string to extendfrom a subsurface terminal therein to the surface terminal,incrementally advancing the well a predetermined amount by manipulatingthe drill string, and for each 2' such advancement adding a length ofpipe provided with an electric conductor section to the drill string tolengthen both the drill string and the electric conductor.

An important advantage of the method of the present invention over priorart techniques is that it reduces the number of connectors required inthe conductor between the subsurface and surface terminals. The combinedlength of conductor sections need not exceed the length of one bit runwhich normally is between about and several thousand feet. This meansthat the portion of the circuit comprising the conductor sections willnormally constitute only a minor fraction of the complete conductor. Formost wells, the conductor installed in accordance with the method of thepresent invention will contain no more than about 30 connectorsregardless of the depth of the well. The substantial reduction in thenumber of connectors increases the reliability of the electric circuitsince each connector presents a potential source of failure. Moreover,the improved method permits the use of conventional drill pipe, which isless expensive than a string of pipe especially made for conductingelectric energy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of welldrilling equipment provided with an electric conductor installed withinthe drill string in accordance with the present invention.

FIG. 2 is an enlarged sectional view of a portion of the drill stringshown in FIG. 1.

FIG. 3 is a transverse sectional view of the assembly shown in FIG. 2with the cutting plane taken along line 33 thereof.

FIG. 4 is an enlarged exploded view, shown in longitudinal section, of acable clamp and connector usable in the conductor shown in FIGS. 1 and2.

FIG. 5 is an enlarged elevation, shown partially in section, of aconnector for joining adjacent conductor sections.

FIGS. 6 and 7 illustrate the manner in which a pipe joint provided witha conductor section is added to the upper end of a drill string.

FIGS. -8, 9, and 10 are schematic illustrations showing the relationshipof the continuous cable and cable sections for successive bit runs in adrilling operation.

FIG. 11 is a longitudinal sectional view of a cable connector capable ofuse in the present invention.

. FIG. 12 is a side elevation of a portion of the connector shown inFIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventional rotary drillingequipment, as schematically illustrated in FIG. 1, includes swivel 10,kelly 11, tubular drill string 12, and bit 13. These components,connected in the manner illustrated, are suspended from the drillingderrick 14 by means of rig hoisting equipment. The kelly 11 passesthrough rotary table 16 and connects to the upper end of the drillstring 12. The term drill string as used herein refers to the column oftubular pipe between the bit 13 and kelly 11; and the term pipe stringrefers to the complete pipe column including the kelly 11. The majorportion of the drill string normally is composed of drill pipe with alower portion being composed of drill collars. The drill string 12consists of individual pipe sections, either drill pipe or drillcollars, connected together in end-to-end relation.

The borehole 17 is advanced by rotating the drill string 12 and bit 13while at the same time drilling fluid is pumped through the drill string12 and up the borehole annulus. The drilling fluid is delivered toswivel through a hose (not shown) attached to hose connection 18 and isreturned to the surface fluid system through pipe 19. A kelly bushing 20couples the rotary table 16 to the kelly 11 and provides means fortransmitting power from the rotary table 16 to the drill string 12 andbit 13. (The use of a power swivel eliminates the need for the kelly androtary table. The present invention may be used with either system; forpurposes of illustration, however, it will be described in connectionwith the kelly and rotary table arrangement.)

As mentioned previously, it frequently is desirable to monitor asubsurface drilling condition during drilling operations. This requiresmeasuring a physical condition at the subsurface location, transmittingthis data as an electric signal to the surface, and reducing the signalto useful form. Typical situations where telemetry is applicable indrilling operations include drilling through abnormal pressure zones,drilling through zones where hole deviation is likely to be a problem,directional drilling, exploratory drilling, and the like.

Although the present invention may be employed in most any drillingoperation wherein an electric conductor is used in tubular pipe totransmit electric energy between a subsurface and surface location, itfinds particularly advantageous application in a wellbore telemetrysystem such as that illustrated in FIG. 1 comprising an instrument 2],conductor 22, and receiver 23.

The instrument 21 capable of measuring a subsurface condition andgenerating an electric signal indicative or representative of thatcondition is mounted or adapted to be mounted in the drill string 12. Avariety ofdevices capable of sensing a physical condition are available.These include transducers for measuring pressure, temperature, strainand the like; surveying instruments for measuring hole deviation; andlogging instruments for measuring resistivity or other properties ofsubsurface formations. The instrument 21 may be powered by batteries orby energy transmitted through conductor 22. Alternatively, a subsurfacegenerator driven by fluid flowing through the drill string 12 may beused to power instrument 21.

The present invention is concerned primarily with the electric conductor22 used to transmit electric energy between surface and subsurfacelocations and a method for installing the same. The energy may be asignal generated by the subsurface instrument 21 and transmitted to thereceiver 23 at the surface. Alternatively, the energy may be electricpower transmitted from the surface to actuate or drive a subsurfaceinstrument or motor. Or, as mentioned previously, energy may betransmitted down the conductor 22 to power the instrument 21, andsimultaneously intelligence may be transmitted up the same conductor.

As applied in telemetry operations, it is preferred that the energybeing transmitted be in the form of a pulsating signal. information canbe transmitted by varying the number, amplitude, width or spacing of atrain of electric pulses, or it can be transmitted by modulating thefrequency or amplitude of the pulsating sig nal. More than onetransducer or other device may be employed in the instrument 21 ifdesired, in which case a multiplexer may be used for sending the varioussignals over a single conductor.

The instrument 21 may be mounted directly in the drill string 12 or, asillustrated in FIG. 1, it may be a separate tool that is lowered intothe drill string 12 on the conductor 22.

The insulated conductor 22 extends from a subsurface terminal oninstrument 21 substantially through the drill string 12, and connects toa suitable surface terminal. The surface terminal in this preferredembodiment is provided by connector 25 of conductor 24. Conductor 24 maybe embedded in the kelly 11, in which case the conductor 22 will extendto the upper end of the drill string 12 and connect to connector 25 atthat point. It is preferred, however, that conductor 24 be disposedwithin kelly 11 as illustrated in FIGS. 1, 6, and 7 and extend a shortdistance, e.g., one to three feet, below kelly 11 and have connector 25at its lower end.

If telemetry operations are to be performed while the kelly 11 and drillstring 12 are rotating, the upper end of conductor 24 will be connectedto a device 26 capable of transmitting electric energy from a rotatingmember to a stationary member. This device may be a rotary transformerhaving a rotor secured to the kelly 11 and a stator secured to thestationary portion of the swivel 10, or it may be a slip ring and brushassembly. Electric conductor 27 and ground conductor 28 interconnect thestationary portion of device 26 and receiver 23. If telemetry operationsare to be performed at times when the drill string 12 and kelly 11 arestationary, the conductors 27 and 28 may be connected directly toconductor 24 through a suitable connector. in this situation, conductors27 and 28 will be disconnected when the kelly 11 and drill string 12 arerotated. Other means for transmitting the signal to the receiver 23include a wireless transmitter connected to conductor 22 and located ona rotating member, e.g. kelly 11.

The receiver 23 is an instrument capable of receiving the signalgenerated by instrument 21 and reducing it to useful form.

In one aspect, the present invention relates to a method forestablishing electric continuity between a subsurface location in a welland maintaining electric continuity as the well is advanced. As notedabove, the method employs an insulated electric conductor disposedinternally of a drill string. The electric conductor will normally beinstalled after the well has been drilled to a depth where wellboretelemetry operations are to commence. This can be as shallow as a fewhundred feet as in the case of directional wells, or several thousandfeet deep. The initial step in the improved method is to lower a drillstring in a well by connecting a plurality of pipe sections together inend-to-end relation. The drill sstring may be used to drill a well as itis lengthened, or the drill string may be simply lowered in a wellalready drilled. Next, a continuous electric conductor 30 (also referredto as cable 30 below) is lowered within the drill string 12 to extendfrom a subsurface terminal, e.g. instrument 21, to a surface terminal,e.g. kelly connector 25. As described in detail below electriccontinuity between the subsurface and surface terminals, is maintainedby adding conductor sections to the continuous conductor 30 as the wellis advanced and as the drill string 12 is lengthened.

The term continuous electric conductor or continuous electric cable asused herein means a length of wire or combination of wires suitable forcarrying electric current. Preferably, the conductor is free ofconnectors, (except for its terminal ends) but as a practical matter itmay be necessary to connect separate lengths of conductors togetherusing electric connectors. A distinguishing characteristic of thecontinuous electric conductor is that it normally includes long spans ofconductor lengths free of connectors and is electrically continuouswhich permits it to be lowered in the drill string in a singleoperation. Preferably, conductor 30 is provided by an armored cable.Armored cable has sufficient strength to permit the use of severalthousand feet of cable and to support the instrument 21 duringrunning-in operations.

The surface equipment for lowering the cable 30 in the drill string 12can be similar to conventional cable handling equipment used in welllogging operations. Such equipment normally includes a power winchhaving a cable wound thereon and a sheave suspended from the rigdrawworks for guiding the cable into or out of the drill string 12.

With the instrument 21 properly located at the desired subsurfacelocation preferably in a suitable sub immediately above the drill bit 13the cable 30 extends internally through the drill string 12 andterminates in a connector 31 at its upper end.

In one embodiment of the invention (illustrated in FIGS. 1-7), the upperend of the continuous cable 30 is supported on a spider 32 or similarsupport secured to the drill string 12. After the continuous cable 30has been lowered in the drill string 12, its upper terminal end providedwith connector 31 is supported on the drill string 12 by means of spider32. As described in detail below, spider 32 may be mounted in the box ofa pipe section, e.g. pipe section 33, of the drill string 12 (see FIG.2). Initially, connector 31 of cable 30 is mated with companionconnector of kelly conductor 24 completing the electric circuit betweeninstrument 21 and receiver 23. The kelly 11 is then attached to thedrill string 12 placing equipment in condition for commencing drillingoperations and permitting wellbore monitoring, if desired. If a cable offixed length is used, it is possible that the connector 31 will not belocated exactly opposite a box end of the top pipe section with thecable 30 properly positioned within the drill string 12. However, thelength of drill string 12 can be made equal to the length of cable 30 byadding short pipe sections at the upper end of the drill string 12.

While drilling operations are in progress, the next pipe section, e.g.pipe section 34 shown in FIGS. 6 and 7, to be added to the drill string12 is placed in a shallow borehole 35 (commonly referred to as mousehole") below the derrick floor. A length of conductor section,preferably a cable section 36, is threaded through pipe section 34.Cable section 36 normally will be slightly longer than pipe section 34and is provided with connectors 37 and 38 at its opposite ends.

When the drilling has proceeded to the point that it becomes necessaryto insert another pipe section in the drill string 12, the kelly 11 anddrill string are elevated, the drill string 12 is supported in therotary table 16, and the kelly 12 separated from the drill string 12.Connectors 25 and 31 are manually separated and the kelly 11 is swungover into alignment with pipe section 34. Connector 25 is mated with theupper exposed connector 37 of cable section 36 and kelly 11 is screwedinto the box of pipe section 34 (See FIG. 7); this assembly is thenelevated above the drill string 12. The length of the cable section 36is such that it extends a short distance, e.g. about one to three feet,below the lower end of pipe section 34, exposing connector 38. Thisconnector is manually mated with connector 31 which again completes thecircuit between the subsurface instrument 21 and the receiver 23. Thepin of pipe section 34 is then screwed into the box of thetop pipesection 33 of the drill string 12. This operation lengthens both thedrill string 12 and the conductor 22 which now comprises cable 30 andcable section 36.

Drilling operations are resumed and the subsurface condition monitoredas desired. The individual sections of drill pipe can be added in themanner described above and illustrated in FIGS. 6 and 7 for eachincremental advance of predetermined length of the borehole 17. Itshould be noted that a spider 32 need not be provided to support theupper end of each cable section. However, a temporary support plate maybe employed to facilitate connecting the cable sections together. Such aplate provided with a radial slot can rest on the box shoulder and beadapted to support a connector thereon. After the connectors of adjacentcable sections are mated, the plate is removed.

Drilling operations will continue with the individual pipe sections 34being added for each incremental advance of the borehole 17 in themanner described above. After drilling has progressed and a number ofpipe sections and cable sections have been added to the system, thelower portion of conductor 22 will be provided by the continuous cable30 and the upper portion by a plurality of cable sections 36 joined inend-to-end relation. This arrangement is illustrated in FIG. 1.Normally, drilling operations will continue in this manner until itbecomes necessary to change the drill bit 13. The number of pipesections and the number of cable sections 36 added during a particularbit run will thus normally be determined by the length of borehole thebit is capable of drilling. This varies within wide limits, but normallyranges from about feet for hard formations to several thousand feet forsoft formations.

There are a number of cables commercially available that can serve ascable 30 and cable sections 36 in the present invention. A particularlysuitable cable is a single conductor, three-sixteenths inch armoredcable manufactured by Vector Cable Company and sold as type I-ISP. Thiscable is sufficiently strong to support long lengths; it has protectivearmor which guards against damage; and it is sufficiently flexible tofacilitate installation.

Since the combined length of the cable sections 36 will normally beshort, these sections in the preferred embodiment of the presentinvention need not be provided with protective armor. Suitable cabletypes include a single conductor, 12 AWG, neoprene jacket conductor soldas 8-5025 by Vector Cable Company. The length of each cable section 36normally will be longer than the average length of pipe section used inthe drill string to compensate for variations in the length of pipesections. The excess length of each cable section also permits the cableto be twisted as pipe sections are screwed together. Moreover, theflexibility of this cable permits cable sections to be overlapped andclamped at the surface or otherwise adjusted to match the length of thepipe sections through which they extend.

As shown in FIGS. 2 and 3, the spider 32 for supporting the upper end ofthe cable 30 is sized to fit into a box end 40 of pipe section 33.Radial arms 41 rest on internal shoulder 42 of the box 40 and an opening43 through the axial center of the spider 32 receives the upper end ofcable 30. The spider 32 should be designed to minimize the flowrestriction through box 40, particularly if internal upset drill pipe isused. A cable clamp 44 comprising sleeves 45 and 46 anchors the armor ofcable 30 as shown in FIG. 4. The cable 30 passes through the centeropening of clamp 44. Wire strands 47 stripped from the armor pass aroundthe upper sleeve 45, through suitable axial openings, and betweenclamping surfaces of sleeves 45 and 46. Tightening the lower sleeve 46on upper sleeve 45 thus firmly secures the wire strands. In theinstalled position, the clamp 44 is supported on the upper surface ofspider 32.

The primary function of the spider 32 is to support the upper end of thecable 30 at a fixed location in the drill string 12. This permits theuse of unarmored, flexible cable sections in the drill string above thespider 32.

In the embodiment of the invention described above, the connectors, e.g.connectors 37 and 38, employed to join adjacent cable section 36 arepreferably plug type connectors. Such connectors are easily installed,provide water-tight connections, and provide adequate strength.Connector 31 (cable 30), connectors 37 and 38 (cable sections 36), andconnector 25 (kelly) may include identical female connectors such asthose illustrated in FIG. 4. A double contact plug 50 which isdetachable from both female connectors but may be considered a part ofeither provides electric continuity through each connection. As shown inFIG. 5, the connection comprising connectors 37 and 38 for joiningadjacent cable sections 36 also includes a double contact plug 53. Forthese connections, it is preferred that a locking sleeve comprising apair of threaded metal halves 51 and 52 be employed. The locking sleeveadds strength to the connection. In this regard, it should be noted thatthe connection for joining a cable section 36 to cable 30 does notinclude a locking sleeve. Thus, the cable sections 36 joined byconnections with locking sleeves can be retrieved as a unit by pullingup on the top cable section 36. Connector 38 will pull free of connector31 permitting the cable sections 36 to be withdrawn from the drillstring in a single operation.

The conductor 22 described above is provided with a single conductor. Insuch a design, the electric ground circuit may be provided by the armorif armored cable is used to the surface, by the drill pipe itself, or bya combination of cable armor and drill pipe. Alternatively, the cable 30and cable sections 36 and connectors may be provided with a plurality ofconductors and contacts.

In describing the operation of the embodiment of the invention describedabove, it will be assumed that the borehole 17 has been drilled to acertain depth using conventional techniques and at this depth it isdesired to commence drilling while logging operations. The drill string12 with bit 13 is lowered into the borehole 17 in the usual manner. Theinstrument 21 is then lowered on cable 30 and located at the properdepth within the drill string 12. The upper end of the cable 30 isprovided with the cable clamp 44 and connector 31. The spider 32 isinserted on the cable 30 immediately below the cable clamp 44. Thisassembly is then seated in the box end 40 of the top section of drillpipe, e.g. pipe section 33. After the kelly connector 25 is mated withconnector 31, the kelly 11 is screwed into the box end 40 placing theassembly in condition for drilling and logging. The borehole 17 isadvanced in increments of predetermined length about equal to length ofpipe to be added to the drill string. Lengths of pipe provided withcable sections 36 are added after each incremental advancement of theborehole in the manner described previously with reference to FIGS. 6and 7. The cable 30 and drill string 12 are thus lengthened together asthe borehole is advanced using conventional drill pipe.

As the drill string is lengthened and as cable sections 36 are added,excess lengths of cable will be introduced into the drill string sinceeach cable section 36 will normally be slightly longer than itscompanion pipe section. Slack can be periodically removed from theconductor by pulling excess cable from the drill string at the surface,overlapping excess lengths, and clamping the overlapped cable in thatconfiguration. Alternatively, spiders can be provided in certain pipesections to prevent excess cable from accumulating and snarling withinthe drill string 12.

When it is desired to interrupt drilling operations, as for example whenit is necessary to change the bit 13, the upper portion of the conductor22 comprising a plurality of cable sections 36 may be retrieved by firstdisconnecting kelly 11 from the drill string 12, then separating kellyconnector 25 from cable connector 37 of the top cable section, andfinally reeling in the string of cable sections 36. Connector 38 securedto connector 31 of cable 30 pulls free separating the string of cablesections 36 from cable 30. The drill string 12 then can be withdrawn inthe usual manner until the pipe section, e.g., section 33, containingthe spider 32 is reached. The continuous cable 30 is then withdrawn byreeling it on a suitable drum. The remainder of the drill string 12 isthen withdrawn in the conventional manner.

The drill string that was withdrawn from the borehole is provided with anew bit and rerun into the borehole. A second continuous cable 30 withinstrument 21 attached to its lower end is then lowered through thedrill string 12 to the instrument setting depth. The second continuouscable may be longer than the previous one by an amount about equal tothe advancement of the borehole made by the previous bit run. A newcable may be employed for this purpose or a length of cable about equalto the advancement of the borehole may be attached to the firstcontinuous cable 30. The equipment is assembled in the manner describedabove, and drilling and telemetry operations resumed. The cable sections36 withdrawn from the drill string may be reused as individual lengthsof pipe are added to the drill string 12.

An important feature of the invention is that the number of connectorsrequired to maintain electric continuity from the subsurface terminal tothe surface terminal need be employed only in a minor fraction of thetotal conductor. This is schematically illustrated in FIGS. 8-10. Forpurposes of illustration, let it be assumed that the well is about 5,000feet where wellbore telemetry operations are to commerce; further, eachbit is capable of drilling about 500 feet. During the initial bit run atthis depth, the borehole is advanced from 5,000 to 5,500 feet. Thisadvancement will be in increments about equal to the length of a pipesection, e.g. about 30 feet. The drill string 12 and conductor 22 arelengthened for each incremental advance in the manner describedpreviously. At the end of the first bit run (see FIG. 8), the continuouscable 30 extends from about 500 to about 5,500 feet and the cablesections 36 connected in end-to-end relation by about 17 connectors(assuming 30-feet joints of drill pipe are used) extend from the top ofthe drill string 12 to about 500 feet. The drill string 12, andconductor 22, are withdrawn from the borehole and the operationsrepeated for a second bit run.

At the end of the second bit run (see FIG. 9), the second continuouscable 30 extends from about 500 feet to about 6,000 feet, or 500 feetmore than the length of the first continuous cable; and the length ofthe cable sections 36 remains about the same, extending from the upperend of the drill string 12 to about 500 feet.

The operations are repeated for a third bit run which is illustrated inFIG. 10, showing the third continuous cable 30 now extending from about500 feet to about 6,500 feet and the cable sections 36 extending fromthe upper end of the drill string to about 500 feet.

These operations may be repeated several times over; or wellboretelemetry operations may be interrupted for several bit runs and resumedat a later time. Of course it will be understood that there will bevariations in the footage that each bit is capable of drilling; that is,some bit runs may be as low as 100 feet or may be as long as 1,000 feetand even longer. It also will be understood that the method is notlimited to the drilling capability of the bit. For example, wellboretelemetry operations may be interrupted for reasons other thanwithdrawing the drill string or replacing the bit. In this regard, itshould be noted that the apparatus disclosed in this preferredembodiment permits the cable sections 36 to be withdrawn from the drillstring 12 enabling drilling operations to continue in the conventionalmanner.

A'comparison of FIGS. 8-10 reveals that lengths of the cable sections 36remain about the same whereas the continuous cable 30 is lengthened foreach bit run. Note that the combined length of cable sections 36 neverexceeds the length of the continuous cable 30. This method thus permitsa substantial reduction in connections required in the conductor overthat required in many prior art techniques. In the above example, only18 connectors were required in each of the three operations. If thecable 30 is lengthened after each bit run by adding a length of cablesection equal to the length drilled by that bit run, one additionalconnector will be required for each successive bit run.

There are a number of arrangements capable of providing the conductorsections in the upper portion of the drill string 12. The conductorsections may be permanently mounted in the drill pipe joints such asthose described in US. Pat. Nos. 3,518,608 and 3,518,609. Preferably,however, the conductor sections are provided by a cable section whichcan be threaded through each length of pipe to be added to the drillstring.

The present invention also contemplates that the upper cable sections 36may be provided by armored cable, in which case the connectors forjoining adjacent cable sections must be adapted to anchor the armor aswell as provide electric continuity across the connection. The use ofarmored cable joined by suitable connectors permits the entire conductorto be supported Y on the kelly cable 24, assuming, of course, that thiscable is also armored and that connector 25 has sufficient mechanicalstrength to bear the weight of the entire conductor string 22.

One embodiment of an armored cable connector suitable for use in thissecond embodiment is shown in FIGS. 11 and 12. The connector assemblydesignated generally as includes a lower body section 56 and an upperbody section 57, each having an axial passage formed therein forreceiving the conductor and connectors. A lower cable section 36 whichin this embodiment will be provided by armored cable extends upward intothe lower end of the body section 56 and terminates in a femaleconnector 62. Strands stripped from the cable section 36 pass throughaxial openings 58 formed in a clamping sleeve 60. The strands areanchored by means of nut 59 threadedly connected to collar 60. Theanchoring assembly is maintained to the lower body section 56 by collar61.

A bulkhead connector 63 is threadedly connected to the interior of thelower body section 56. The pin (not shown) of the bulkhead connector 63extends downwardly and mates with the female connector 62. An 0- ring 64positioned at the base of the bulkhead connector provides a fluid tightseal between the connector 63 and body section 56. A second bulkheadconnector 65 is also threadedly connected to the interior of the lowerbody section 56 and is provided with an upwardly extending pin (notshown). This connector is also provided with an O-ring 66 at its base.An insulated conductor 67 interconnects the interior contacts ofbulkhead connectors 63 and 65.

A second, upper armored cable also illustrated as 36 in FIG. 11 extendsdownwardly into the upper body section 57 and is similarly provided witha cable anchor comprising sleeve 68, nut 69, and collar 70. Theconductor wire of cable 36 extends through the upper body section 57terminating in the female connector 71. Connector 71 is maintained inplace by bushing 72.

The lower and upper body sections 56 and 57 are separable and areadapted to be joined by coupling 73. Coupling 73 is mounted on the upperbody section 57 for relative rotation thereon, and it is provided withinternal threads adapted to mate with external threads formed on thelower body section 56. A spring-loaded locking sleeve 74 is alsoprovided to insure that the parts are maintained in assembled relation.The locking sleeve 74 includes a lug 75 adapted to fit snugly into acomplementary shaped recess 76 formed in the lower edge of coupling 73(See FIG. 12). The locking sleeve 74 is mounted for relative axialmovement on the body section 56. The connection between the lockingsleeve 74 and body v56 may be splined or grooved so as to preventrelative rotational movement.

The female connectors 62 and 71 may be similar to those illustrated inFIG. 4.

During drilling operations, the cable sections 36 may be joined in themanner described previously with ref erence to FIGS. 6 and 7. With theupper cable section 36 positioned above an adjacent cable section (eachcable section being provided with complementary halves of the connectorassembly 55) the connector 71 is mated with the pin of bulkheadconnector 65. The

coupling 73 is then screwed onto the lower body section 56, and finallythe locking sleeve 74 which has been maintained in a retracted position,is moved upwardly until the lug 75 enters the recess 76 formed in thelower edge of collar 73. As cable sections 36 are added to the conductor22, it may be necessary to remove slack from the conductor. This may beachieved by periodically overlapping a portion of a cable section toremove slack from the conductor and securing the overlapped portions; orby using spiders as described above.

Although the present invention has been described with reference toconventional rotary drilling operations, it can also be used with othertypes of drilling equipment including turbo drills and positivedisplacement hydraulic motors. These devices normally include a motor orturbine mounted on the lower end of the drill string and adapted toconnect to and drive a bit. The motor or turbine powered by the drillingfluid drives the drill bit while the drill string remains stationary.When this type subsurface drilling device is used in directionaldrilling operations, the present invention provides a highly usefulmeans for transmitting directional data to the surface.

I claim:

1. A method of establishing and maintaining electric continuity betweena subsurface terminal in a well and a surface terminal which comprises:

a. lowering a pipe string in said well by connecting a plurality of pipesections together in end-to-end relation;

b. lowering a first electric conductor in said pipe string to establishelectric continuity between said subsurface terminal near the lower endof said pipe string and said surface terminal;

c. repeatedly advancing said well by an amount sufficient to requirelengthening said pipe string;

d. for each of such advancements, adding a length of pipe to said pipestring and a conductor section to said first electric conductor.

2. A method as defined in claim 1 wherein said first electric conductoris substantially free of connectors.

3. A method as defined in claim 1 wherein said first electric conductorcomprises armored cable.

4. A method as defined in claim 2 wherein each of said conductorsections comprises insulated electric cable free of armor.

5. A method as defined in claim 2 wherein the combined length of theconductor sections added according to step (d) is less than the lengthof said first conductor.

6. A method of establishing and maintaining electric continuity betweena subsurface location within a well and the surface which comprises:

a. lowering in said well a pipe string comprising a plurality of pipesections connected together in endto-end relation;

b. lowering in said pipe string a continuous electric cable to establishelectric continuity from a subsurface terminal and a surface terminal;and

c. advancing said well in increments of predetermined length and foreach incremental advancement, lengthening said pipe string and saidelectric cable by: threading a cable section through a length of pipe tobe added to said pipe string;

connecting said cable section to the upper end of the cable in saiddrill string and said surface terminal; and

connecting said length of pipe into said pipe string.

7. A method as defined in claim 6 wherein the step of lowering saidcontinuous electric cable in said pipe string includes supporting theupper end of said continuous electric cable on said pipe string.

8. A method as defined in claim 6 wherein the total length of cablesections added to the electric cable according to step (c) never exceedsthe length of said continuous electric cable.

9. A method of drilling a well while maintaining an electric circuitbetween a subsurface location in said well and the surface whichcomprises:

a. lowering a pipe string in said well, said pipe string comprising aplurality of pipe sections;

b. lowering a first electric cable into said pipe string, said firstelectric cable establishing electric circuit between a subsurfaceterminal near the lower end of said pipe string and a surface terminal;

0. repeatedly advancing said well in increments sufficient to requirelengthening said pipe string, and for each increment so advanced,lengthening said pipe string and electric cable in said pipe string bydisconnecting said pipe string and separating electric cable at thesurface, threading an electric cable section through a length of pipe,connecting said cable section with the electric cable in the pipe stringto reestablish the electric circuit between said terminals, andconnecting the length of pipe into said pipe string, the total length ofsaid cable sections being less than the length of said first electriccable.

10. A method as recited in claim 9 and further comprising:

d. withdrawing said pipe string so lengthened, said first electriccable, and said cable sections from said well;

e. lowering said pipe string withdrawn in step (a) into said well; and

f. lowering a second electric cable into said pipe string, said secondelectric cable being substantially longer than said first electric cableand extending from a subsurface terminal near the lower end of said pipestring to a surface terminal; and

g. repeatedly advancing said well in increments sufficient to requirelengthening said pipe string, and for each increment so advancedlengthening said pipe string and electric cable in said pipe string bydisconnecting said pipe string and electric cable at the surface,threading an electric cable section through a length of pipe, connectingsaid cable section with electric cable in the pipe string to reestablishthe electric circuit between said terminals, and connecting the lengthof pipe into said pipe string, the total length of said cable sectionsbeing less than the length of said second electric cable.

11. A method of maintaining an electric conductor within a pipe stringused to drill a well which comprises:

a. lowering a continuous electric cable through a pipe string whichcomprises a plurality of pipe sections disposed in a well to provide anelectric conductor between a subsurface terminal near the lower end ofsaid pipe string and a surface terminal;

13 14 b. supporting the upper end of said cable on said pipe cable insaid pipe string to extend said conductor g; and thereby reestablishingelectric continuity berepeatedly advancing Said in increments of tweensaid subsurface and surface terminals, and predetermined fimoum; andinserting said length of pipe into said pipe to d. for each of saidadvancements, lengthening said lengthen Said pipe String pipe String andthe electric conductor therein by 12. A method as recited in claim 11and further addisconnecting said pipe string and separating electriccable contained therein at the Surface thread usting the length of atleast one cable section used to ing flexible electric cable section freeof protective extend Said electric conductor in Said Pip String to armorthrough a length of pipe to be inserted in the move ce s ack rom Saidcable sections. pipe string, connecting said cable section with

1. A method of establishing and maintaining electric continuity betweena subsurface terminal in a well and a surface terminal which comprises:a. lowering a pipe string in said well by connecting a plurality of pipesections together in end-to-end relation; b. lowering a first electricconductor in said pipe string to establish electric continuity betweensaid subsurface terminal near the lower end of said pipe string and saidsurface terminal; c. repeatedly advancing said well by an amountsufficient to require lengthening said pipe string; d. for each of suchadvancements, adding a length of pipe to said pipe string and aconductor section to said first electric conductor.
 2. A method asdefined in claim 1 wherein said first electric conductor issubstantially free of connectors.
 3. A method as defined in claim 1wherein said first electric conductor comprises armored cable.
 4. Amethod as defined in claim 2 wherein each of said conductor sectionscomprises insulated electric cable free of armor.
 5. A method as definedin claim 2 wherein the combined length of the conductor sections addedaccording to step (d) is less than the length of said first conductor.6. A method of establishing and maintaining electric continuity betweena subsurface location within a well and the surface which comprises: a.lowering in said well a pipe string comprising a plurality of pipesections connected together in end-to-end relation; b. lowering in saidpipe string a continuous electric cable to establish electric continuityfrom a subsurface terminal and a surface terminal; and c. advancing saidwell in increments of predetermined length and for each incrementaladvancement, lengthening said pipe string and said electric cable by:threading a cable section through a length of pipe to be added to saidpipe string; connecting said cable section to the upper end of the cablein said drill string and said surface terminal; and connecting saidlength of pipe into said pipe string.
 7. A method as defined in claim 6wherein the step of lowering said continuous electric cable in said pipestring includes supporting the upper end of said continuous electriccable on said pipe string.
 8. A method as defined in claim 6 wherein thetotal length of cable sections added to the electric cable according tostep (c) never exceeds the length of said continuous electric cable. 9.A method of drilling a well while maintaining an electric circuitbetween a subsurface location in said well and the surface whichcomprises: a. lowering a pipe string in said well, said pipe stringcomprising a plurality of pipe sections; b. lowering a first electriccable into said pipe string, said first electric cable establishingelectric circuit between a subsurface terminal near the lower end ofsaid pipe string and a surface terminal; c. repeatedly advancing saidwell in increments sufficient to require lengthening said pipe string,and for each increment so advanced, lengthening said pipe string andelectric cable in said pipe string by disconnecting said pipe string andseparatIng electric cable at the surface, threading an electric cablesection through a length of pipe, connecting said cable section with theelectric cable in the pipe string to reestablish the electric circuitbetween said terminals, and connecting the length of pipe into said pipestring, the total length of said cable sections being less than thelength of said first electric cable.
 10. A method as recited in claim 9and further comprising: d. withdrawing said pipe string so lengthened,said first electric cable, and said cable sections from said well; e.lowering said pipe string withdrawn in step (a) into said well; and f.lowering a second electric cable into said pipe string, said secondelectric cable being substantially longer than said first electric cableand extending from a subsurface terminal near the lower end of said pipestring to a surface terminal; and g. repeatedly advancing said well inincrements sufficient to require lengthening said pipe string, and foreach increment so advanced lengthening said pipe string and electriccable in said pipe string by disconnecting said pipe string and electriccable at the surface, threading an electric cable section through alength of pipe, connecting said cable section with electric cable in thepipe string to reestablish the electric circuit between said terminals,and connecting the length of pipe into said pipe string, the totallength of said cable sections being less than the length of said secondelectric cable.
 11. A method of maintaining an electric conductor withina pipe string used to drill a well which comprises: a. lowering acontinuous electric cable through a pipe string which comprises aplurality of pipe sections disposed in a well to provide an electricconductor between a subsurface terminal near the lower end of said pipestring and a surface terminal; b. supporting the upper end of said cableon said pipe string; c. repeatedly advancing said well in increments ofpredetermined amount; and d. for each of said advancements, lengtheningsaid pipe string and the electric conductor therein by disconnectingsaid pipe string and separating electric cable contained therein at thesurface, threading flexible electric cable section free of protectivearmor through a length of pipe to be inserted in the pipe string,connecting said cable section with cable in said pipe string to extendsaid conductor and thereby reestablishing electric continuity betweensaid subsurface and surface terminals, and inserting said length of pipeinto said pipe to lengthen said pipe string.
 12. A method as recited inclaim 11 and further adjusting the length of at least one cable sectionused to extend said electric conductor in said pipe string to removeexcess slack from said cable sections.